The invention relates to a method for controlling a projection exposure apparatus for microlithography, embodied as a scanner, in the exposure operation. Furthermore, the invention relates to a projection exposure apparatus for microlithography.
In the case of projection exposure apparatuses embodied as scanners, a reticle is moved along a scanning axis with respect to a frame of the projection exposure apparatus during the exposure operation such that the reticle is scanned by an illumination field radiated thereon. The scanned reticle surface is thereupon imaged on a wafer via a projection lens. As a result of such an exposure during the scanning operation, a desired dose distribution is generated on the wafer, which dose distribution emerges from the intensity distribution radiated onto the individual points of the wafer and integrated over the time of the exposure process.
However, there are often irregularities in the dose distribution radiated onto the wafer during the scanning operation. That is to say, the distribution of the dose accumulated by the wafer during a scanning process deviates from a desired intended distribution.
Underlying Object
It is an object of the invention to provide a method for controlling a projection exposure apparatus for microlithography and a projection exposure apparatus, via which the aforementioned problems are solved, and, in particular, irregularities in the dose distribution radiated onto the wafer can be kept as small as possible.
Solution According to the Invention
By way of example, according to the invention, the aforementioned object can be achieved by a method for controlling a projection exposure apparatus for microlithography, embodied as a scanner, in the exposure operation. In this exposure operation, a reticle is moved along a scanning axis with respect to a frame of the projection exposure apparatus such that the reticle is scanned by an illumination field radiated thereon, and the radiation of the illumination field is guided onto a wafer after interaction with the reticle in order to generate a desired dose distribution on the wafer. The method comprises the following steps: measuring positional changes of the illumination field in the direction of the scanning axis with respect to the frame of the projection exposure apparatus, and correcting the influence of a measured positional change of the illumination field on the dose distribution on the wafer by modifying at least one operational parameter of the projection exposure apparatus.
Here, the dose distribution on the wafer should be understood to mean a spatial distribution of the integrated intensity impinging on the wafer during the exposure operation, in which a scanning process is carried out. The integrated intensity should be understood to mean the intensity accumulated at a respective point of the wafer during the whole scanning process. This accumulated intensity is referred to as dose.
In other words, according to the method according to the invention, the position of the illumination field relative to the frame of the projection exposure apparatus is monitored in the direction of the scanning axis, i.e. in the scanning direction or opposite to the scanning direction. If a positional modification occurs, at least one operational parameter of the projection exposure apparatus is modified, to be precise in such a way that an effect on the dose distribution generated on the wafer during the exposure operation is corrected by modification of the operational parameter. Operational parameters which can be corrected can, for example, comprise the intensity of the radiation generating the illumination field and/or a scanning speed of the projection exposure apparatus, as explained in more detail below.
The solution according to the invention is based on the insight that a positional modification of the illumination field in the direction of the scanning axis can lead to the observed irregularities in the dose distribution radiated onto the wafer. The correction according to the invention leads to the situation where displacements in the illumination field, which occur during the exposure operation, do not lead, or only lead to a small extent, to irregularities in the dose distribution radiated onto the wafer.
As a result, the method can, for example, serve to correct an illumination instability of a radiation source of the projection exposure apparatus, leading to the illumination field, which is also referred to as illumination slit below, being displaced on the reticle in the direction of the scanning axis.
By way of example, such displacements occur in EUV illumination systems. In these systems, pupil facets are used to image field facets onto the reticle. If there is a change in the angular distribution of the light on the field facets, this leads to a modification in the reticle illumination. This angular distribution is primarily given by the spatial position of the source plasma of the EUV source. If the source plasma moves, this changes the angular distribution on the field facets, which in turn leads to a modification in the illuminated field position on the reticle. Such a modification of the illuminated field position can, in particular, lead to a positional change of the illumination field, which in turn leads to the dose errors on the wafer, as mentioned at the outset.
In accordance with one embodiment according to the invention, in order to correct the influence of the measured positional change of the illumination field on the dose distribution on the wafer, the emission intensity of the radiation generating the illumination field is modified. In particular, this is brought about by modifying the emission intensity of a radiation source which generates the radiation of the illumination field.
In accordance with one embodiment variant, in the case where the direction of the measured positional change of the illumination field corresponds to the movement direction of the reticle, the correction is brought about by reducing the intensity of the radiation generating the illumination field.
In accordance with a further embodiment according to the invention, in the exposure operation, the wafer furthermore carries out a scanning movement and, in order to correct the influence of the measured positional change of the illumination field on the dose distribution on the wafer, the speed of the scanning movement of the wafer is modified.
In accordance with one variant or embodiment, in the case where the direction of the measured positional change is opposite to the movement direction of the reticle, the correction is brought about by reducing the speed of the scanning movement of the wafer, and, in particular, by also reducing the speed of the scanning movement of the reticle.
In accordance with a further embodiment according to the invention, the positional changes of the illumination field are measured via a sensor module, which is configured for a spatially resolved intensity measurement.
In accordance with one variant of embodiment, the illumination field is generated by an illumination system of the projection exposure apparatus and the spatially resolving sensor module is arranged between the illumination system and the reticle. In other words, the spatially resolving sensor module is arranged in a region which lies between the last optical element of the illumination system and the reticle. In accordance with one embodiment, the measurement is arranged in the region of the reticle.
In accordance with a further embodiment, the spatially resolving sensor module has a detection region, which extends at least over the whole extent of the illumination field in the direction of the scanning axis.
In accordance with one variant of embodiment, the spatially resolving sensor module has sensor elements arranged in succession in the direction of the scanning axis, of which sensor elements two sensor elements are arranged in such a way that they respectively adjoin a respective peripheral region of the illumination field. Such sensor elements can be read out separately. The two sensor elements adjoining the peripheral region can, for example, either both be arranged within the illumination field or both be arranged outside of the illumination field. The specifications in respect of the arrangement of the sensor elements in relation to the illumination field or the peripheral region thereof relates to the situation in which the illumination field is in an intended position.
In accordance with a further embodiment according to the invention, the spatially resolving sensor module has at least three sensor elements arranged in succession in the direction of the scanning axis, wherein a central one of the sensor elements has a detection area, the extent of which is a multiple of the extent of the respective detection area of the other sensor elements. In accordance with one variant of embodiment, the detection area of the central sensor element extends over the whole extent of the illumination field in the direction of the scanning axis.
In accordance with a further embodiment according to the invention, the spatially resolving sensor module comprises a detection region and has a spatial resolution of at least 500 μm in at least one section of the detection region. In other words, the spatially resolving sensor module has at least one sensor element which can be read out separately, the detection area of which is less than or equal to 500 μm. In accordance with one variant or embodiment, the spatially resolving intensity sensor has at least five, in particular at least six, at least seven, at least ten or at least fifteen, sensor elements arranged in succession in the direction of the scanning axis.
In accordance with a further embodiment according to the invention, in the exposure operation, the reticle is moved backward and forward a number of times within a scanning region and the modification of the at least one operational parameter is undertaken within a period of time in which the reticle, after a positional change has taken place, is moved on by at most 10% of the length of the scanning region, in particular by at most 5% of the scanning length.
In accordance with a further embodiment according to the invention, the modification of the at least one operational parameter takes place within less than 10 milliseconds (ms), in particular within less than 8 ms, 5 ms, or 4 ms, after measuring the positional change.
Furthermore, according to the invention, provision is made for a projection exposure apparatus for microlithography, which comprises an illumination system for radiating an illumination field onto a reticle, a frame and a reticle displacement device which is configured for moving the reticle with respect to the frame along a scanning axis in such a way that the reticle is scanned by the illumination field. The projection exposure apparatus furthermore comprises a projection lens for generating a desired dose distribution on a wafer from the radiation of the illumination field after interaction with the reticle, a measuring device, which is configured to measure positional changes of the illumination field in the direction of the scanning axis with respect to the frame of the projection exposure apparatus, and a control device. The control device is configured to correct the influence of a measured positional change of the illumination field on the dose distribution on the wafer by modifying at least one operational parameter of the projection exposure apparatus.
Moreover, according to the invention, provision is made for a projection exposure apparatus for microlithography, which comprises an illumination system for radiating an illumination field onto a reticle and a reticle displacement device for moving the reticle backward and forward within a scanning region, wherein the reticle displacement device can be operated with a predetermined maximum scanning speed. Moreover, the projection exposure apparatus according to the invention comprises a control device, which is configured to convert a measurement signal relating to the radiated illumination field into a control signal for controlling an operational parameter of the projection exposure apparatus within a period of time during which the reticle displacement device is moved over at most 10% of the length of the scanning region, in particular over at most 5% of the length of the scanning region, at the maximum scanning speed. To this end, the control device contains correspondingly fast control electronics.
In accordance with one embodiment of the projection exposure apparatus, the control device is configured to convert the measurement signal into the control signal in less than 10 ms.
In accordance with a further embodiment, the projection exposure apparatus according to the invention is designed for exposure in the EUV wavelength range.
In accordance with a further embodiment according to the invention, the measuring device comprises a sensor module which is configured for the spatially resolved intensity measurement. In accordance with one variant of embodiment, the spatially resolving sensor module has a detection region, which extends at least over the whole extent of the illumination field in the direction of the scanning axis. In accordance with a further variant or embodiment, the spatially resolving sensor module has sensor elements arranged in succession in the direction of the scanning axis, of which sensor elements two sensor elements are arranged in such a way that they respectively adjoin a respective peripheral region of the illumination field. In accordance with a further variant or embodiment according to the invention, the spatially resolving sensor module has at least three sensor elements arranged in succession in the direction of the scanning axis, wherein a central one of the sensor elements has a detection area, the extent of which is a multiple of the extent of the respective detection area of the other sensor elements. In accordance with one embodiment according to the invention, the spatially resolving sensor module comprises a detection region and has a spatial resolution of at least 500 μm in at least one section of the detection region.
The features specified in respect of the embodiments, exemplary embodiments or embodiment variants of the method according to the invention, listed above, can be transferred accordingly to the projection exposure apparatus according to the invention in one of the specified variants. Conversely, the features specified in respect of the embodiments, exemplary embodiments or embodiment variants of the projection exposure apparatus according to the invention, listed above, can be transferred accordingly to the method according to the invention. These and other features of the embodiments according to the invention will be explained in the claims and in the description of the figures. The individual features can be realized either separately or in combination as embodiments of the invention. Furthermore, they can describe advantageous embodiments which are independently protectable and protection for which is claimed, if appropriate, only during or after pendency of the application.